1. Field of the Invention
The present invention relates to a surface treatment method, and in particular relates to a surface treatment method for a sprayed coating film formed on a surface of an electrostatic chuck.
2. Description of the Related Art
Substrate processing apparatuses are known that carry out plasma processing such as etching processing on wafers as substrates. Such an apparatus has a housing chamber in which a wafer is housed, and a stage that is disposed in the housing chamber and on which the wafer is mounted. In the substrate processing apparatus, plasma is produced in the housing chamber, and the wafer is subjected to the etching processing by the plasma.
The stage has in an upper portion thereof an electrostatic chuck comprised of an insulating member having an electrode plate therein, the wafer being mounted on the electrostatic chuck. While the wafer is being subjected to the etching processing, a DC voltage is applied to the electrode plate, the electrostatic chuck attracting the wafer thereto through a Coulomb force or a Johnsen-Rahbek force generated by the DC voltage (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H05-190654).
Moreover, a coolant chamber is provided inside the stage. A coolant, for example cooling water or a Galden fluid, at a predetermined temperature is supplied into the coolant chamber from a chiller unit. A processing temperature of the wafer attracted to and held on a surface of the electrostatic chuck is controlled through the temperature of the coolant.
Conventionally, the electrostatic chuck is subjected to surface treatment as shown in FIGS. 4A and 4C. First, a sprayed coating film is formed on the surface of the electrostatic chuck by thermally spraying with a ceramic such as alumina (FIG. 4A) . The sprayed coating film is shown enlarged in FIG. 4B. Next, a grindstone obtained by compacting together abrasive grains and making into a disk shape is brought into contact with the surface of the electrostatic chuck on which the sprayed coating film has been formed. The grindstone is then rotated, and also moved parallel to the surface of the electrostatic chuck on which the sprayed coating film has been formed. The electrostatic chuck is also rotated about an axis of rotation shown by the alternate long and short dash line in FIG. 4C. As a result, the surface of the electrostatic chuck is ground, i.e. processed, as shown enlarged in FIG. 4D.
However, as shown in FIG. 4D, an electrostatic chuck processed using the conventional method has a rough surface when viewed microscopically, and furthermore there are minute undulations on the surface of the electrostatic chuck. A wafer attracted to and held on the electrostatic chuck contacts the surface of the electrostatic chuck, and hence the temperature of the wafer depends on the contact area between the wafer and the surface of the electrostatic chuck. If the surface of the electrostatic chuck is rough, then the contact area between the wafer and the surface of the electrostatic chuck is low, and hence the thermal contact resistance of the contacting portion becomes high. In this case, when controlling the processing temperature of the wafer, in particular when reducing the temperature of the wafer, a high-performance chiller unit must be used.
Moreover, in recent years, with the diversification of semiconductor devices, a variety of etching characteristics have come to be required, for example there are cases in which it is required to realize etching at a low wafer temperature under high-density, high-ion energy plasma conditions. Under such high-density, high-ion energy plasma conditions, much heat is inputted into the wafer, and hence the temperature of the wafer increases greatly. To achieve both high-density, high-ion energy plasma and a low wafer temperature, it is thus necessary to use a chiller unit that can produce an extremely low temperature and hence has a high power consumption.
Moreover, in recent years, due to etched shapes becoming finer and more complex, etching processes have come to be divided into a plurality of steps, it being required to control the wafer temperature with good response when changing steps. However, in the case of a conventional electrostatic chuck, because the thermal contact resistance between the wafer and the surface of the electrostatic chuck is high, the wafer temperature cannot be controlled with good response by controlling the temperature of the coolant from the chiller unit. Moreover, even in the case of using, for example, a heater or a Peltier element as a temperature control device for the wafer in the electrostatic chuck, the wafer temperature still cannot be controlled with good response.
Moreover, conventionally, as a method of improving the efficiency of heat transfer between the wafer and the surface of the electrostatic chuck, a method of introducing a heat transfer gas in between the wafer and the surface of the electrostatic chuck has been proposed. However, with this method, to satisfy the above requirements on the etching characteristics, the pressure of the heat transfer gas must be greatly increased, so that in some cases the wafer may become detached from the electrostatic chuck. As a countermeasure, one can envisage increasing the value of the DC voltage applied to the electrode plate of the electrostatic chuck so as to increase the wafer attracting force. However, in this case, the voltage resistance of the insulating member of the electrostatic chuck must be increased, and setting the thickness of the insulating member which is a layer above the electrode plate in the electrostatic chuck so as to achieve both a good wafer attracting force and a good insulating member voltage resistance is difficult from a design perspective. The insulating member generally has a worse heat transfer coefficient than a metal, and hence if the insulating member is made thicker so as to increase the voltage resistance, then there is a problem that the efficiency of heat transfer becomes poor in this region.